Long weekend-- roughly between Frankfurt and Bonn

There's a reason there's only one boat from Mainz. Skip the dull part of the river by taking a train to Bingen, where 4 K-D cruise boats depart daily. Scroll down for schedule:

https://www.k-d.com/fileadmin/KD_Fahrplaene/KD_Fahrplan_intern_2024_web.pdf

Cruise to St. Goar. In the morning make your way to the clifftops before it gets too hot to enjoy the hike up and along the Rhine Castle trail in the direction of Oberwesel. You'll have scenery here that includes the Loreley cliffs on the opposite river bank. It's close to 3 hours to reach Oberwesel on foot, take the train back to St. Goar... or return at some point on foot to St. Goar as you came.

A northbound train should get you to Rolandseck, where the Arp Museum is located:

https://www.tripadvisor.com/Attraction_Review-g642105-d729455-Reviews-Arp_Museum-Remagen_Rhineland_Palatinate.html

Train to Bonn after that.

Forget the ferry, just take the train. You can go from Bingen to Koblenz easy. And the train stops in St Goar and Boppard, as well as Bachrach and Oberwesel. You can get off wherever you want and walk the small town, eat, drink, shop or just sit and watch the river traffic. There's another train every 30 minutes all day long.

Take the RE2, RE17, or RB26. The ticket will run about 20 euros.

I was hoping to get a KD ferry

I should have addressed the terminology in my first post.

If you use the word "ferry" (Fähre in German) in Germany, Germans will think you are referring to a vessel like this one in St. Goar, whose only task is to shuttle people and cars back and forth across a lake or river.

There are several ferry crossings on this part of the Rhine, which are marked by the red symbol (with a car and 2 foot passengers) on this map:
https://www.youtube.com/watch?v=ph8qTKBlmJE

Use the word "ship" (Schiff in German) to be best understood when referring to day-cruise boats like K-D's.

There's a reason there's only one boat from Mainz. Skip the dull part of the river by taking a train to Bingen, where 4 K-D cruise boats depart daily. Scroll down for schedule: https://www.k-d.com/fileadmin/KD_Fahrplaene/KD_Fahrplan_intern_2024_web.pdf Cruise to St. Goar. In the morning make your way to the clifftops before it gets too hot to enjoy the hike up and along the Rhine Castle trail in the direction of Oberwesel. You'll have scenery here that includes the Loreley cliffs on the opposite river bank. It's close to 3 hours to reach Oberwesel on foot, take the train back to St. Goar... or return at some point on foot to St. Goar as you came.

Thank you, this is really helpful, good to know the scenery starts to get interesting from Bingen, and that there are them more cruise boat options

Use the word "ship" (Schiff in German) to be best understood when referring to day-cruise boats like K-D's.

really helpful tip, thank you. I never would have used that, and actually probably would have avoided using the word "ship" in searching anything because there are so many multi-day cruises on the Rhine that it's hard to find info on the type of thing I want to do.

If we do take a KD schiff, say from Bingen to St Goar, will there be enough space for bags? We will each have a backpack/rucksack that is cabin bag sized (not tiny underseat, but not a massive hiking backpack, either). I don't know if many people actually use these for transport between hotels, or if it's more generally just a day-trip.

Forget the ferry, just take the train. You can go from Bingen to Koblenz easy. And the train stops in St Goar and Boppard, as well as Bachrach and Oberwesel. You can get off wherever you want and walk the small town, eat, drink, shop or just sit and watch the river traffic. There's another train every 30 minutes all day long.

Definitely happy to consider this, thank you, are the trains at all scenic? Just putting that route in, I guess it does look like it's a much quicker journey on train, so presumably we could get the train from Mainz to Koblenz (or St Goar or wherever we will overnight) and then if we wanted to do a KD schiff could do it as an excursion from there?

I wonder if there's any likely towns where we could hire a bike or an e-bike to ride one way and pay the KD supplement for bikes to get back on the water?

The trains run right along the river, so there's something to look at all the way along the trip, except at the very top when it goes inland a bit to get into Koblenz.

You could easily stay in one of the towns (like St Goar) and then catch another train the next day. But to take a day trip on a ship you'd want to leave from Bingen or Rüdesheim, and then plan a trip back (or onward). The problem with those is they don't stop at all the towns, and you have to plan to accommodate their schedule. The train is much more flexible.

Contact "Bike Service Bingen" about leasing a bike. You might also consider just buying a used bike and then leaving it at the train station at the end of your trip. I've done that in a couple towns before I bought my current ebike (in Nancy a used bike cost 30 Euro.) You can take bikes on the train (look for the bike symbol as to what cars you can use). There is a bike route along the river that parallels the train and highway. You can Google the route.

Carry-on bags on K-D: Should be no problem. I've seen oversized bags at times, lots of carry-on size packs with bags with rollers, The site gives a written thumbs up to hand-baggage, in the FAQ's under "Bicycles and Luggage" ...
https://www.k-d.com/en/faq

Cruise Discount: show the train ticket you used to reach Bingen at the KD kiosk for a 20% price break.

Cruise ship v. train: It's the rare piece of advice suggesting that the Rhine Gorge scenery is better enjoyed by train. Sure, Bingen > St. Goar is faster by train - but are you in a hurry? Greater speed of course means what you are able to see out the window is going by fairly quickly. AND... what you are able to see, if you are sitting on the correct side of the train, and if the windows are nice and clean, is still limited; the trains run alongside the river on a narrow spit of land, often right up against the cliffside - which means that what you see out the window on one side is nothing but a bunch of rocks and dirt racing by, or buildings doing the same in a rapid blur. The only view of the castles, vineyards, towns etc. you might have is the view of the east bank. Cruising right down the middle of the river in the fresh air at a leisurely pace - with both sides of the gorge in view - is really the finest way to do this.

That doesn't mean you shouldn't use the train. Check your time tables... once in St. Goar, you are only 5 train minutes from Oberwesel, and 5 more from Bacharach. There's no reason in the world why you shouldn't visit these very nice old-world towns by train if you wish to - sometime AFTER you've stepped off your cruise boat in St. Goar. A DB ticket from St. Goar to Bacharach is priced at €5.60 and allows you travel at any time and to make a stopover in Oberwesel if you wish. Sample schedule...

11:15 cruise Bingen > St. Goar (ar. approx. 13:00.)
Drop bags at hotel. Find lunch. Visit Rheinfels Castle?

15:56 or 16:56: train to Oberwesel (16:01 or 17:01) for a 1.5 hr. walk around town

17:26 or 18:26: train to Bacharach for the same (and dinner?)

19:50 or 20:50: train from Bacharach to St. Goar (10-min. train ride.)

Thank you both, I'll look into all of those options and will probably be back with more questions!

One more from me in the meantime-- it turns out we have hotel points that we could use to stay free in Mainz. Would it be silly to spend two nights there rather than one midway between Frankfurt and Bonn? It looks like trains are pretty quick and assume we could do excursions around the more scenic parts and then go back to Mainz, but don't know if that is a waste of time on transport.

2 nights in Mainz:  For your time on the Rhine I outlined a one-day cruise + St. Goar/Oberwesel/Bacharach strategy. So you could in fact leave your bags in Mainz on that Saturday morning, carry out that strategy, and return to Mainz that evening instead of staying in your St. Goar hotel. But it will require an hour or so of backtracking that night, with additional backtracking by train on Sunday morning when you head towards Bonn...

"Sunday make our way to end up in Bonn, again ideally with some time enjoying the views of what I understand is gorgeous scenery."

The question that arises is how you plan to spend your Sunday. Will that be the day you do some hiking or biking, or tour castles (like Marksburg, in Braubach?) or do a chairlift ride (like the one pictured, in Boppard) or visit the Arp museum (Rolandseck)??

In addition to the backtracking, the additional problem with a Saturday night stay in Mainz will be managing your luggage on Sunday. The small towns on the Rhine don't have locker facilities for your bags. TI offices, which sometimes keep bags for visitors, don't remain open on Sundays, typically. But if instead you stay in St. Goar - or nearby Boppard - you should be able to leave bags with your hotel while pursuing your Sunday activities. Pick them up later that pm when you are ready to catch a train to Bonn (roughly 1.5 hours from St. Goar.)

Thanks Russ, yes I was wondering about the luggage question, that's a helpful point! I will do more research on where we might stay in that area and see if I can find something that would work for both of us.

Another option would be to see if you can use points in Koblenz, and stay there at the end of your Rhine excursions. But that would mean moving your luggage along with you.

Another option would be to see if you can use points in Koblenz, and stay there at the end of your Rhine excursions. But that would mean moving your luggage along with you.

Yes, I am looking at options in Koblenz, although none of the hotels we have points at have branches there, sadly! We won't have so much luggage that it's a problem to have with us getting between places and hopefully can drop bags at the hotel even if it's too early to check in.